A typical ink jet printer has a pen that reciprocates over a printable surface such as a sheet of paper. The pen includes a print head having an array of numerous orifices through which droplets of ink may be expelled onto the surface to generate a desired pattern. Some ink jet printers have a replaceable ink supply mounted to a stationary position on the printer, and connected to a reciprocating print head by a conduit. This permits the use of a larger ink supply, and avoids the need to replace the print head each time the supply of ink is depleted. Color ink jet printers generally have several ink supply cartridges each containing a different color of ink, or a multi-chamber cartridge.
Printers with remote or "off axis" ink supplies are normally shipped with the ink supplies and print head removed. The ink conduit is empty, open to ambient air, or in a "dry" condition. This avoids potential leakage of the ink and shelf life reduction that begins when the seal of an ink supply cartridge is penetrated. More significantly, if ink were to remain in the ink conduit for an extended period between manufacturing and first use, air may be absorbed by the ink, and water evaporated. This would undesirably change the consistency of the ink beyond normal parameters. In addition, the print head may be protected in special packaging against potential shocks during shipping. When printers are shipped "dry," the ink conduits are empty, except for the presence of ambient air.
When setting up such a printer for its first use, as ink flows from the ink supply to the print head and its on-board reservoir, the air volume within the ink tube is forced into the print head reservoir. If the reservoir is sufficiently large, this can be readily accommodated, but leaves a substantial air volume in the reservoir. Thereafter, ambient pressure or temperature variations, such as caused by changing weather or air travel, can generate pressure changes in the air bubble that undesirably force ink from the orifices. The consequences of such leakage or "drool" include user inconvenience, printer damage, and impaired printing.
Current systems may address this problem with a startup or "dummy" printhead that is removed after air in the tubes is displaced by ink, then replaced by the user with a functional pen for printing. Such startup printheads may have a receptacle to accept air from the tubes, possibly including a suction device to inhale the air, and to draw ink into the tubes. Another system uses a Porex.RTM. self sealing porous plastic element on the dummy pen. When ink is pumped from the ink supplies to the pen to prime the tubes, air in the tubes is released through the porous element to the atmosphere. When the tubes are essentially full, ink reaches the porous element and wets it, sealing it against further emission of fluid or additional gas. Then, the startup printhead is removed by the user and replaced with a standard printhead.
While effective, such systems have certain disadvantages. In some cases, an inexperienced user may mistakenly remove the startup printhead without conducting the priming step. Such errors cause the new printhead to be filled with air, possibly rendering it unusable. Even when the startup printhead is properly used, the replacement process is a moderate inconvenience, and may be somewhat messy, due to residual ink on the startup printhead.
The present invention overcomes the limitations of the prior art by providing an ink jet printer having a body with a paper path and a carriage operable to reciprocate across the paper path. An ink supply receptacle on the body is spaced apart from the carriage, and an ink conduit extends between the ink supply receptacle and a fluid output interconnect on the carriage. A gas release facility connected to the conduit allows air to be released from the conduit when the printer is first to be used. This may occur in response to filling the conduit with ink, and the facility may be near the carriage end of the conduit to allow substantial evacuation of air from the conduit. The facility may prevent further release of gas or fluid when wet, such as provided by a porous polymer material.